Properties of Nonlinear Solitary Structures in Astrophysical and Space Plasmas

Holmes, Justin C.

Graduate Thesis Or Dissertation

Properties of Nonlinear Solitary Structures in Astrophysical and Space Plasmas Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/pz50gw16t

Abstract

Solitary waves are a commonly observed form of strong electric fields parallel to the back- ground magnetic field in space plasmas. It has been repeatedly suggested that they have a significant influence on the surrounding environment, either individually or as a collective. At a minimum, nonlinear waves appear to be signposts for important plasma processes such as magnetic reconnec- tion and turbulence. Understanding the effects of solitary waves on the macro-scale first requires us to characterize their structure on the micro-scale. In this thesis, I examine solitary waves of several flavors using a combination of simulations and high time resolution data from the Magnetospheric MultiScale (MMS) mission. Timing between multiple spacecraft is used to precisely measure the structures’ size and speed. In all cases, solitary waves defy our expectations based on ideal physical models. In one instance, a type of solitary wave known as an electron phase-space hole is found to have structure in its perpendicular electric field which is not predicted by existing 3D models. In another case, I identify unusually large-scale, quasi-neutral structures which have a combination of properties expected from both electron solitons and ion phase-space holes. Their parallel velocity and size perpendicular to the background magnetic field are on electron scales despite having nearly equal ion and electron density perturbations. Simulations reproducing nonlinear wave observations contribute to a growing body of evidence that difficult to observe, low energy, ‘cold’ features in the electron distribution can drive instabilities capable of growing into nonlinear waves and structures. In the relativistic case, electron hole formation may lead to further instabilities which produce coherent radiation — potentially visible in astrophysical observations or distributing energy via resonant heating. These discoveries open up new possibilities for modeling the role of solitary waves in particle acceleration, plasma heating, and radio emission.

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